1. Field of the Invention
The present invention relates to a power-saving radio communication system and a base station for use in the radio communication field.
2. Description of the Related Art
In the radio communication system where many communication devices such as mobile phones are used, the Personal Digital Cellular (PDC) communication in the second generation is based on voice applications. Beginning with the Code Division Multiple Access (CDMA) method and the Wideband CDMA (W-CDMA) method in the third generation, the data communication evolves into the mobile Internet access data communication. In addition, the commercial services have begun where the Evolution Data Only (EV-DO) method or the High Speed Downlink Packet Access (HSDPA) method, designed specifically for data communications, are used. There is an increasing need for high-speed communications in a radio communication system, with the high-speed radio infrastructure being built using the next-generation high-speed radio methods such as Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX).
In the conventional mobile phone system, the macro cell method is used where one base station covers a large area. Commercial services are beginning to be offered that combines the macro cell method with the femtocell method in which a base station is installed to cover the area of one building to improve the radio environment in the building where the radio wave from a macro cell is difficult to reach. Recent advances in the broadband technology allow high-speed communication lines, such as Fiber to the Home (FTTH) lines and Asymmetric Digital Subscriber Line (ADSL) lines, to be widely used, introducing the high-speed communication environment into the home. The introduction of such high-speed access line infrastructure begins to draw attention to the femtocell base station service that uses high-speed access lines.
A macro base station, which accommodates multiple terminals at the same time, performs operations with the power constantly on. On the other hand, a femtocell base station, which covers a small area sometimes with no terminal in the area, does not have to keep the power constantly on. Therefore, when a femtocell base station is installed in a home, power saving is required to reduce the electricity expense.
The well-known power saving technology is the intermittent reception operation employed by a terminal. This technology reduces the power consumption by intermittently removing the power for a fixed period during the reception. However, a femto base station, which serves as a base station that must respond to random access from the terminals, cannot use the intermittent reception operation. In addition, a femto base station must regularly transmit the information signal to notify the terminals of the presence of the femto base station.
JP-A-2010-004438 discloses the technology in which, with the transmission of the electric wave stopped, the radio communication transmission/reception unit receives the electric wave from a radio communication terminal and, after determining from the received electric wave signal that the radio communication terminal that has transmitted the electric wave is an authorized terminal, starts the transmission of the electric wave.
JP-A-2009-159355 discloses the technology in which a neighboring base station or a macro base station, which finds that there is a terminal in its cell, notifies the femto base station of the presence of the terminal to cause the femto base station to start the transmission.